1. Field of the Invention
The present invention generally relates to a method for processing magneto-resistive random access memory (MRAM) film stacks. More specifically, the invention relates to a method for removal of residue after plasma etching a magneto-resistive random access memory (MRAM) film stack using a photoresist/silicon dioxide dual mask.
2. Description of the Related Art
Microelectronic devices are generally fabricated on a semiconductor substrate as integrated circuits. An example of such a device is a magneto-resistive random access memory (MRAM) wherein magnetic multilayer films, or film stacks, are used as storage elements. The magnetic multi-layer films are typically a stack of different layers composed of various materials, for example permalloy (NiFe), cobalt iron (CoFe), tantalum (Ta), copper (Cu) and the like, and may also contain insulator materials such as aluminum oxide as a thin tunneling layer sandwiched between the multi-layers. The layers are typically deposited in overlying blanket films, layer by layer, and then featured. One of the typical processes used during feature fabrication is plasma etching, in which one or more layers comprising a film stack are removed, either partially or in total to form a feature.
During the plasma etching process, a metal film (or film stack) is etched using a plasma, for example a plasma comprising fluorine or chlorine chemistry. In such an example, the fluorine or chlorine from the etchant combines with the removed metal to form a residue. For example, if a film contains tantalum, a plasma etch process utilizing chlorine (Cl2) will form tantalum chloride (TaCl) residue. Additionally, if a carbon-based photoresist is used during metal etching, a metal-containing polymer may also form as an additional residue resulting from the etch process.
The residues typically deposit or redeposit along the sidewalls of the layer or film stack. These residues, for example, can be redeposition of the material just removed from the layer along the sidewalls of the film or film stack. Additionally, the residues may include a by-product of the plasma etchant reacting with the removed metal and this by-product residue being deposited along the sidewalls of the film or film stack. Such residues may build up along the sides of the film or film stack above the upper surface of the film or film stack, forming a “veil” like structure.
Residues containing metal, metal chlorides, fluorides, oxides and polymers interfere with further processing of the film or film stack. These residues may contaminate any additional films or layers that are deposited upon the remaining metal and/or the film or film stack. Additionally, the residues, and especially the veil-like structures, can cause electrical short-circuits, for example as between the two magnetic layers separated by a thin tunneling layer within a MRAM device, and other problems, as well as causing film stack irreproducibility.
Therefore, there is a need in the art for a method of removing residues after plasma etching a magneto-resistive random access memory (MRAM) film stack.